Compartment syndrome is a medical condition where the pressure inside a compartment, which is a muscle group surrounded by fascia or a thin, inelastic film, increases until the blood circulation inside the volume defined by the fascia or thin film is cut off. The most common site, in humans, occurs in the lower leg, and more specifically, in regions adjacent to the tibia and fibula. There are four compartments in the lower, human leg: the anterior (front), lateral (side next to the fibula) and the deep and superficial posterior (back).
These four compartments surround the tibia and fibula. Anyone of these four compartments can yield a compartment syndrome when bleeding or swelling occurs within the compartment. Compartment syndrome usually occurs after some trauma or injury to the tissues, such as muscles or bones or vessel (or all three), contained within the compartment. Bleeding or swelling within a compartment can cause an increase in pressure within that compartment. The fascia does not expand, so as pressure rises, the tissue and vessels begin to be compressed within the compartment.
This compression of tissue, such as muscle, due to intra-compartmental pressure can restrict and often times stop blood flow from entering the compartment that is destined for any tissues contained within the compartment. This condition is termed ischemia. Without blood flow to tissues, such as muscle, the tissues will eventually die. This condition is termed necrosis.
A simple working definition for a compartment syndrome is an increased pressure within a closed space which reduces the capillary blood perfusion below a level necessary for tissue viability. As noted above, this situation may be produced by two conditions. The first condition can include an increase in volume within a closed space, and the second condition is a decrease in size of the space.
An increase in volume occurs in a clinical setting of hemorrhage, post ischemic swelling, re-perfusion, and arterial-venous fistula. A decrease in size results from a cast that is too tight, constrictive dressings, pneumatic anti-shock garments, and closure of fascial defects. As the pressure increases in tissue, it exceeds the low intramuscular arteriolar pressure causing decreased blood in the capillary anastomosis and subsequent shunting of blood flow from the compartment.
The clinical conditions that may be associated with compartment syndrome include the management of fractures, soft tissue injuries, arterial injuries, drug overdoses, limb compression situations, burns, post-ischemic swelling, constrictive dressings, aggressive fluid resuscitation and tight casts.
Referring now to the Figures, FIG. 1 illustrates an X-ray view of a human leg 100 with fractured bones of the tibia 105 and fibula 110 that lead to one or more compartment syndromes in the muscles 115 surrounding the bones of the human leg 100. The tibia 105 and fibula 110 usually bleed in regions proximate to the physical break regions 120. This bleeding can form a large pool of stagnant blood referred to as a hematoma. The hematoma can start pressing upon muscles 115 that may be proximate to the break 120. This pressure caused by the hematoma can severely restrict or stop blood flow into the muscles 115 of a compartment, which is the diagnosis of a compartment syndrome.
Traditional Methods for Diagnosing Compartment Syndromes
Referring now to FIG. 2, this Figure is a side view of a human leg 100 in which compartment pressures are being measured with a large bore needle 200, having a gauge size such as 14 or 16 (which is the largest needle in the hospital available to clinicians), according to a conventional method known in the prior art. While compartment pressures can be measured with this conventional method, the method is highly invasive procedure which can cause tremendous pain to the patient. Needles with large gauge sizes of 14 or 16 are analogous to sticking a patient with an object as large as a nail or a pen.
In addition to causing tremendous pain to the patient, there are several more problems associated with the conventional needle measuring method. First, it is very challenging for a medical practitioner to actually measure or read pressure of a compartment since the needle must be positioned at least within the interior of a compartment. To enter the interior of a compartment, the needle 200 must penetrate through several layers of skin and muscle. And it is very difficult for the medical practitioner to know if the needle has penetrated adequately through the intermediate layers to enter into the compartment. This challenge significantly increases if the patient being measured is obese and has significant amounts of subcutaneous fat in which to penetrate with the needle.
Often, the medical practitioner may not have a needle accurately positioned inside a compartment which can yield a reading of the tissue adjacent to the compartment, such as muscle or skin. Such a reading of muscle or skin instead of the compartment of interest can provide the medical practitioner with elevated or depressed pressure readings that do not reflect the actual pressure contained within the compartment of interest. Pressure readings inside a compartment have been shown to vary (increase) based on the depth of the reading as well as the proximity to the fracture site.
Because of the challenge medical practitioners face with precisely positioning a needle within a compartment of interest and because of the numerous law suits associated with the diagnosis of compartment syndrome, many medical schools do not provide any formal training for medical practitioners to learn how to properly place a needle within a compartment of interest for reading a compartment's pressure. Therefore, many medical practitioners are not equipped with the skills or experience to accurately measure compartment pressures with the needle measuring method.
Currently, intra-compartmental pressures are the only objective diagnostic tool. Due to the legal climate regarding this condition, clinicians are forced to treat an elevated value for compartment pressures or expose themselves to legal ramifications with any complications. As described later, the treatment of compartment syndrome can cause significant morbidity and increase the risk for infection. Therefore inaccurate and elevated pressure readings are a very difficult and potential dangerous pitfall.
Another problem associated with the training and experience required for the needle measuring method is that, as noted above, compartment syndromes usually occur when tissues within the compartment are experiencing unusual levels of swelling and pressure. With this swelling and pressure, the tissues do not have their normal size. Therefore, any training of a medical practitioner must be made with a patient suffering under these conditions. A normal patient without any swelling would not provide a medical practitioner with the skills to accurately assess a size of a compartment when using the needle measuring method for determining compartment pressure. Put another way, due to the trauma associated with the injury, normal anatomy is not always present when attempting to measure compartment pressures.
In addition to the problem of entering a compartment that may have an abnormal size or anatomy, the needle measuring method has the problem of providing only a snap-shot of data at an instant of time. When the conventional needle measuring method is used, it provides the medical practitioner with pressure data for a single instant of time. In other words, the needle pressure method only provides the medical practitioner with one data point for a particular time. Once pressure is read by the medical practitioner, he or she usually removes the needle from the patient. The data obtained from a single measurement in time gives no information concerning the pressure trend, and the direction the intra-compartmental pressure is moving.
This collection of single data points over long periods of time is usually not very helpful because pressures within a compartment as well as the patient's blood pressure can change abruptly, on the order of minutes. Also, because of the pain associated with the needle measuring method noted above, the medical practitioner will seldom or rarely take pressure readings within a few minutes of each other using a needle.
A further problem of the needle measuring method is that for certain regions of the body, such as the lower leg, there are four compartments to measure. This means that a patient's leg must be stuck with the large bore needle at least four times in order for a medical practitioner to rule out that a compartment syndrome exists for the lower leg. In the lower leg of the human body, one compartment is located under a neighboring compartment such that a needle measurement may be needed in at least two locations that are very close together, but in which the medical practitioner must penetrate tissues at a shallow depth at a first location to reach the first compartment; and for reaching the second compartment that is underneath the first compartment, a large depth must be penetrated by the needle, often with the needle piercing the first compartment and then the second compartment.
Another problem, besides pain that is associated with the needle pressure measuring method, is that there is a lack of consensus among medical practitioners over the compartment pressure ranges which are believed to indicate that a compartment syndrome may exist for a particular patient. Normal compartment pressure in the human body usually approaches 4 mmHg in the recumbent position. Meanwhile, scientists have found that an absolute pressure measurement of 30 mmHg in a compartment may indicate presence of compartment syndrome. However, there are other scientists who believe that patients with intracompartmental pressures of 45 mmHg or greater should be identified as having true compartment syndromes. But other studies have shown patients with intra-compartmental pressures above these limits with no clinical signs of compartment syndrome. Additional studies have shown that a pressure gradient based on perfusion pressure (diastolic blood pressure minus intra-compartmental pressure) is the more important variable. Studies have shown in a laboratory setting that once the perfusion pressure drops to 10 mm Hg tissue necrosis starts to occur.
Other subjective methods for diagnosing compartment syndromes instead of the needle measuring method exist, however, they may have less accuracy than the needle measuring method because they rely on clinical symptoms of a patient. Some clinical symptoms of a patient used to help diagnose compartment syndromes include pulselessness (absence of a pulse), lack of muscle power, pain, parastesias, and if the flesh is cold to touch. Pain out of proportion and with passive stretch are considered the earliest and most sensitive, but both have very low specificity. One of the major drawbacks of these symptoms is that for many of them the patient must be conscious and must be able to respond to the medical practitioner. This is true for the muscle power and pain assessment. For any inebriated patients or patients who are unconscious, the pain assessment and muscle power assessment cannot be used accurately by the medical practitioner. In the setting of high energy trauma which is associated with compartment syndrome, many patients are not capable of cooperating with a good physical exam due to any number of causes including head trauma, medical treatment (including intubation), drug or alcohol ingestion, neurovascular compromise or critical and life threatening injuries to other body systems.
For the pain assessment, if a lower leg compartment syndrome exists in a patient, then the range of motion for a patient's foot or toes will be extremely limited and very painful when the patient's foot or toes are actively or passively moved. The pain from a compartment syndrome can be very immense because the muscles are deprived of oxygen because of the compartment syndrome.
Another drawback using pain to assess the likelihood of a compartment syndrome is that every human has a different threshold for pain. This means that even if someone should be experiencing a high level of pain, he or she may have a high threshold for pain and therefore, not provide the medical practitioner with a normal reaction for the current level of pain. Another problem with using pain to assess the likelihood of the existence of a compartment syndrome is that if the patient is experiencing trauma to other parts of their body, he or she may not feel the pain of a compartment syndrome as significantly, especially if the trauma to the other parts of the patient's body is more severe. This condition is termed a distracting injury. On the other hand, trauma causes the initial injury that precipitates a compartment syndrome. That initial trauma by definition will cause a baseline amount of pain that is often very difficult to separate from a potential compartment syndrome pain. These initial injuries by themselves cause significant pain, so a patient that does not tolerate pain well may present similar to a compartment syndrome without having any increased pressures simply because they react vehemently to painful conditions.
Conventional Non-Invasive Techniques for Measuring Oxygenation Levels of a Compartment
Non-invasive measuring of compartment syndromes using near infrared sensors, such as spectrophotometric sensors, to measure oxygenation levels within a compartment has been suggested by the conventional art. However, these conventional techniques have encountered the problem of a medical practitioner locating compartments of interest and accurately and precisely positioning a sensor over a compartment of interest. Often the orientation of the scan and the depth of the scan produced by a near infrared sensor as well as the orientation of a compartment can be challenging for a medical practitioner to determine because conventional sensors are not marked with any instructions or visual aids. Another problem faced by the medical practitioner with conventional non-invasive techniques is determining how to assess the oxygenation level of compartments that lie underneath a particular neighboring compartment, such as with the deep posterior compartment of the human leg.
In trauma settings, near infrared sensors often do not work when they are placed over regions of the body that have hematomas or pools of blood. In such conditions, a medical practitioner usually guesses at what regions of the human body do not contain any hematomas that could block compartment measurements. Also, conventional near infrared sensors typically are not sterilized and cannot be used in surgical or operating environments.
Near infrared sensors (NIRS) in their current form are limited to a single sensor with a single sensor depth. They also can be affected by skin pigmentation that is not accounted for in the current technology. Placement of the sensor can be difficult since an expanding hematoma can block a previously acceptable placement. Additionally, the only system as of this writing is a single monitor system. There is no product available at this time which will allow for multiple areas to be monitored in close proximity to one another without the potential for interference from other sensor light sources.
Treatment for Compartment Syndrome
Referring now to FIG. 3, this figure is a side view of a human leg 100 in which a surgical procedure, known as a fasciotomy, was performed in order to release the pressures in one or more compartments surrounding the bones of the leg according to a technique known in the art in order to alleviate a compartment syndrome that was diagnosed. This surgical procedure includes an incision 300 that is made along the length of the leg 100 and is generally as long as the compartments contained within the leg 100. While a single incision 300 is illustrated in FIG. 3, a second incision is made on the opposing side of the leg so that a patient will have two incisions on each side of his leg 100. These incisions typically extend from near the knee to near the ankle on each side of the leg.
This procedure is very invasive and it often leaves the patient with severe scars and venous congestion once healed. Also the procedure increases a patient's chances of receiving an air-borne infection because the incisions made on either side of the leg are usually left open for several days in order to allow for the swelling and excess bleeding to subside. Fasciotomies transform a closed fracture (one in which the skin is intact and minimal risk of infection) to an open fracture. Open fractures have a much higher risk of bone infections which requires multiple surgical debridements and ultimately amputation in some cases in order to appropriately treat. Additionally, some wounds cannot be closed and require skin transfers, or skin grafts, from other parts of the body, usually from the anterior thigh.
Therefore, it is quite apparent that accurately diagnosing compartment syndrome is critical because any misdiagnosis can lead to significant morbidity. A missed compartment syndrome can result in an insensate and contracted leg and foot. A fasciotomy which is highly invasive procedure and which exposes a patient to many additional health risks should not be performed in the absence of a compartment syndrome.
Additionally, time is an important factor in the evaluation of these patients. Ischemic muscle begins to undergo irreversible changes after about six hours of decreased perfusion. Once irreversible changes or necrosis occur, a fasciotomy should not be performed. Fasciotomies in the setting of dead muscle only increase the risk for severe infections and other complications. Late fasciotomies have been shown to have approximately a 50-75% risk of complication. Therefore, fasciotomies need to be performed early but judiciously in patients that are often unresponsive or uncooperative in order to prevent severe morbidity.
Accordingly, there is a need in the art for a non-invasive, real time method and system that monitors oxygenation levels of a compartment and that is provided with sensors which can be precisely positioned over a compartment of interest in order to assist in assessing conditions associated with a compartment syndrome. A further need exists in the art for a non-invasive method that monitors oxygenation levels of a compartment over long periods of time at frequent time intervals and that can monitor different compartments that may be in close proximity with one another. Another need exists in the art for oxygenation sensors that can be fabricated to fit the size of compartments of interest. There is also a need in the art for a non-invasive method and system that monitors oxygenation levels and that can identify ideal locations along a human body in which to conduct scans for deep compartments. There is another need in the art for sterile, non-invasive oxygenation sensors that can be used under surgical and operating conditions. There is a need for multiple locations and multiple compartments to be monitored in a continual and orchestrated manner by a single system. In other words, multiple monitors coordinated to limit noise and continually monitor multiple compartments are needed in the art.